This application claims the priority of European patent application no. 00 109 342.6, filed May 2, 2000, the disclosure of which is incorporated herein by reference in its entirety.
The present invention relates to new thixotropic agents for viscous systems, in particular for the manufacturing of adhesives and sealants with migration-free properties.
For the production of non-sag viscous systems thixotropic agents are used. Inorganic fillers such as e.g. carbon black, aerosil etc. are used. Achieving thixotropy by means of such fillers usually leads to an increase in viscosity and therefore such fillers are primarily considered for the production of compositions for mechanical processing. For the manual processing, e.g. out of a cartridge, the compositions are preferably rendered non-sag by means of organic thixotropic agents since such organic thixotropic agents cause almost no viscosity increase. Organic thixotropic agents are e.g. amide waxes, hydrolyzed castor oils, or urea derivatives that are produced in an inert carrier such as plasticizers, hydrocarbons etc. Such inert carriers, however, have the disadvantage that they can migrate even out of cross-linked systems, such as one-component polyurethane systems, thereby leading to a deterioration of quality. Dependent on the situation, this can have several consequences: For an adhesive, loss of adhesion may result; Substances diffusing out of the composition may cause health problems, a visual deterioration of porous substrates etc.
Thus, the present invention aims at providing new thixotropic agents for adhesives and sealants that overcome the above mentioned drawbacks.
Hence, it is a general object of the invention to provide a thixotropic agent based on at least one urea derivative in a migration-free carrier material.
Another object is a viscous, at least one curable binder comprising system containing a thixotropic agent of the present invention.
Still another object is a method for the production of the thixotropic agent of the present invention.
The thixotropic agents of the present invention arexe2x80x94as some thixotropic agents of the state of the artxe2x80x94based on urea derivatives. However, for the production of the thixotropic agents of the present invention a non-migrating carrier is used. Such a carrier is either intermingled or interwoven with the structure matrix after the cross-linking, has pronounced compatibility with the whole system, or is incorporated into the structure matrix and can therefore not diffuse out of the cured material. The carrier material or parts thereof should not show any migration tendency on white cement.
Carrier materials suitable in the scope of the present invention are those that do not show any migration according to the test method specified below: The thixotropic agent, or an adhesive or sealing composition comprising such thixotropic agent, respectively, are applied to white cement in form of beads. After 7 days curing at 23xc2x0 C. and 50% relative humidity (r.h.), the contact zone of the adhesive bead to the substrate is visually examined for signs of migration. Thixotropic agents or carriers, respectively, that under the above mentioned conditions show no noticeable migration, will be referred to below as non-migrating etc.
The thixotropic agents of the present invention are suitable for any cross-linking system. Such cross-linking systems can be two-component systems that cross-link upon mixing of a binderxe2x80x94also referred to as resin componentxe2x80x94with a curing agent. The resin component contains reactive groups such as acrylate groups, epoxy groups, isocyanate groups, silane groups, etc. Possible curing agents are e.g. amino groups or hydroxy groups or sulfur groups comprising compounds, initiators for initiating a polymerization of activated double bonds, water, catalysts, etc. The cross-linkable system can also be a one-component system that can be cured either thermally by air humidity or by radiation such as UV-radiation.
The chemistry for the production of urea derivatives is known (see e.g. DE 1805693) and is preferably based on the reaction of aromatic, monomer diisocyanates (isocyanate monomer), such as 4,4xe2x80x2-diphenylmethylene diisocyanate (=MDI), with an aliphatic amino compound, such as e.g. butyl amine. Since both compounds, the isocyanate as well as the amine, are highly reactive, immediately after the mixing of the components the urea derivative is formed as a solid in the carrier material. In the scope of the present invention, the high reactivity of the two reactants requires a careful choice of process parameters and an optimal selection of the carrier material, preferably a reactive carrier material, in order to exclude or at least minimize undesired side reactions as far as possible. The urea derivative can be present in the carrier material in concentration of 5 to 50% or more, preferably in the range of 15 to 30%, and the content is dependent on the processability of the resulting thixotropic agent.
For the production of the thixotropic agent of the present invention, the influence of water present in the carrier material must be considered in the stoichiometric calculation of the amount of isocyanate monomer, such as MDI, and of the amine compound.
Non reactive carrier materials are long-chain polymers with high affinity for the cross-linkable, or the cross-linked system. Said affinity can possibly be enhanced by suitable substitution, such that migration of the carrier material in the cross-linked system does not occur.
Preferred carrier materials are reactive carrier materials such as polyols, blocked isocyanate polymers (prepolymers terminated with blocked isocyanate groups), silane groups terminated prepolymers and/or acrylate groups comprising polymers.
Preferred polyols are polyols with an OH-value of  less than 28 mg KOH/g or a Mw per OH-group of  greater than 2000, respectively, more preferably polyols with an OH-value of  less than 10 mg KOH/g or a MW per OH-group of  greater than 6000, whereby such polyols much preferably are liquid at a temperature of about 20xc2x0 C.-25xc2x0 C.
It is also within the scope of the present invention that the carrier material is a mixture of carrier materials with the same or different reactivity, in particular a combination of a prepolymer comprising acrylate groups with a prepolymer on silane basis.
The production of the thixotropic agents of the present invention can be carried out in various ways. Two possible production methods, using illustrative examples for polyol prepolymers, are disclosed below in greater detail. In an analoguous manner, said methods can be applied to blocked isocyanate prepolymers and silane groups terminated prepolymers. The production of thixotropic agents with non-reactive carrier materials is less critical since undesired side reactions are excluded.
In a first method at least one isocyanate monomer is added to a mixture of at least one amine compound and at least one polyol. Another procedure is that at least one isocyanate monomer is dissolved in at least one polyol, and is immediately added to a mixture of at least one amine compound in the same palyol(s), optimally in an equivalent ratio of isocyanate:amine of 1:1. Experiments have shown that the quality of the resulting thixotropic agent is dependent on the OH-value since the isocyanate monomer immediately reacts with the hydroxyl groups of the polyol. A good quality results if the OH-value is below 28 mg KOH/g, preferably below 10 mg KOH/g, or the molecular weight per OH-group is above 2000. in particular above 6000.
Preferably, the polyol is liquid at room temperature, or at about 20 to 25xc2x0 C., respectively, in order to avoid the costly preheating of the polyol on the one hand, and on the other hand, to avoid a removal of additional heat resulting from the pre-heating step during the exothermic production of the urea derivative. Polyethers are particularly suitable as polyols. If the polyol is a polyethylene glycol, the inventive thixotropic agent can serve as basis for a water swellable sealant.
Mercapto groups comprising compounds are hardly suitable as carrier materials since they are even more reactive towards isocyanate groups than hydroxyl groups and significantly lead to undesired side reactions. In a further embodiment, thixotropic agents of the present invention comprising polyols as carrier material can be reacted with an isocyanate compound such as monomer dilsocyanate compounds, isocyanatomethacrylate, isocyanatoproplsilane etc., whereby said polyol carrier is convened into a binder or into a carrier material terminated with reactive groups, e.g., a carrier material terminated with isocyanate groups.
In a further method for the production of an inventive thixotropic agent, a blocked isocyanate prepolymer is used, in place of the polyol. Such blocked isocyanate prepolymers are e.g. described in Progress in Organic Coatings, 3 (1975) 73-99, or Progress in Organic Coatings, 9(1981) 3-28. Since said blocked isocyanate groups cannot react with the amine, their concentration and therefore their chain length is not critical. A thixotropic agent so produced, is suitable for heat reactive systems, whereby the blocking group is liberated due to the heat treatment, and the deblocked isocyanate group reacts with a H-active compound such as e.g. OH-groups, NH-groups, SH-groups etc. These H-active groupsxe2x80x94dependending on the H-active groupxe2x80x94may contain additional functional groups such as epoxy groups, silane groups, acrylate groups, etc.
Furthermore, silane groups terminated binders, such as MS-polymer (MS=modified silicone) of Kaneka, or a silane groups terminated polyurethane hybrid prepolymer, can also be used as carrier material. A thixotropic agent of the present invention with silane groups terminated carrier material is preferably used as isocyanate-free system, or in isocyanate-free systems on silane basis. Such prepolymers are e.g. described in the patent documents EP 0 355 426, U.S. Pat. No. 3,627,722, DE 40 29 505, U.S. Pat. No. 5,364,955, EP 0 918 062 and U.S. Pat. No. 5,910,555.
In a further embodiment of the present invention, at least one isocyanate monomer can be dissolved in at least one polymer comprising acrylate groups, and added to at least one amine compound that is dissolved in a silane based prepolymer. Such polymers comprising acrylate groups are e.g. obtained by reaction of prepolymers comprising isocyanate groups with hydroxy(meth)acrylate (see e.g. EP 0 675 144).
It is of course possible and within the scope of the present invention to use one carrier material or mixtures of carrier materials. Such mixtures of carrier materials can comprise materials of the same or different reactivity. All reactivities have to be determined beforehand in order to e.g. reduce undesired side reactions by xe2x80x9cdilutingxe2x80x9d respective reactive groups (see polyols). Side reactions can also be reduced by using an optimized production method, e.g. by using a multi-component mixing device.
It is also within the scope of the present invention to use one isocyanate monomer or a mixture of isocyanate monomers, and one amine or a mixture of amines.
The thixotropic agents of the present invention can be applied either directly as system containing viscous, curable binders, or further binders, as well as other components such as fillers, plasticizers, adhesion promoters, catalysts, UV-stabilizers, and/or usual additives can be added, whereby such additional binders are not limited to the binders described as carrier materials, but can alsoxe2x80x94depending on the carrier materialxe2x80x94comprise binders with reactive groups such as epoxy groups, isocyanate groups, acrylate groups, and/or silane groups. Furthermore, the thixotropic agents of the present invention can comprise a curing component, in particular a latent curing agent that can be activated by humidity and/or heat.
The inventive thixotropic agents of the present invention are particularly suitable because they lead only to an insignificant or no increase in viscosity, and furthermore show no tendency to bleed-out or migrate.
Examples are shown below that are intended to further illustrate the invention, but they are not intended to restrict the scope of the invention in any way.